Posted: Fri, May 19, 2006, 8:15 AM ET (1215 GMT)
NASA officials have decided to use the RS-68 engine, and not a derivative of the Space Shuttle Main Engine (SSME), on the first stage of its planned heavy-lift Cargo Launch Vehicle (CaLV), a key element of the agency's exploration architecture. NASa has decided to use five RS-68 engines in the core stage of the CaLV rather than a similar number of SSMEs after concluding that the RS-68 would be cheaper: the engine, currently used on the first stage of the Delta 4, costs $20 million each, a "dramatic cost savings" over an SSME-derived alternative, according to a NASA statement. Both engines are built by Pratt & Whitney Rocketdyne. Switching to the RS-68 will require widening the core stage propellant tanks from 8.4 to 10 meters in diameter because of the additional propellant required by the engines. The decision means that the SSME will likely be retired when the shuttle fleet is retired in 2010: NASA earlier decided to use a derivative of the Apollo-era J-2 engine on the second stage of the Crew Launch Vehicle (CLV), rather than a modified SSME.

Related Links:

•  NASA press release